A typical computer system uses clock signals to synchronize operations of digital circuitry of the system. Unfortunately, spectral components of these clock signals may contribute to the radiation of electromagnetic interference (EMI) emissions from the system. The EMI emissions may cause undesirable interference with the circuitry of the computer system and other electronic equipment near the computer system. To reduce the EMI emissions outside of the computer system, the circuitry of the computer system may be housed inside a metal casing that prevents the EMI emissions from propagating outside of the casing. However, the casing often adds to the weight and cost of the computer system, and the casing may have a limited EMI shielding capability.
The EMI emissions may be reduced by spread spectrum clocking (SSC), a technique that reduces the energy peaks present in the spectral components of the clock signal. In SSC, a spread spectrum clock signal may be generated by an SSC generator. SSC is widely deployed in the video data transfer interface, such as low-voltage differential signaling (LVDS), Transition-minimized differential signaling (TMDS) and Mobile Industry Processor Interface Display Serial Interface (MIPIDSI), in order to suppress its pixel clock (PCLK) oriented radio frequency (RF) emission and its interference to RF application. SSC usually modulates PCLK cycle. As the PCLK is the unit time of one pixel data transfer, the SSC application moderates the video timing cycle, such as one horizontal (1H) line access cycle as well as one frame update cycle. In a certain display device application, such as, for example, Active Matrix organic light-emitting diode (OLED), the 1H cycle modulation causes each line brightness variation, observed as the visual artifact.